cansync: Sync two CAN logs of the same bus from different hosts

[Notgnoshi]

Goals:

• Identify time synchronization offsets - how close are the system clocks?
  • How does this change if the socket is using hardware timestamps?
• Identify dropped frames
  • These might be dropped by userspace (candump / candumpr itself) or by the kernel / transceiver?
• Optional goal: Given a bunch of files from multiple devices, figure out which files overlap with each other (this isn't phrased well; I don't have a good idea of what this actually means in practice, nor do I have a concrete enough use-case to motivate it)

Challenges:

• We're not guaranteed every frame in one log will be in another (error frames, dropped frames)
• We're not guaranteed both log files start at or even near the same time (could range from a few seconds to a few hours)
• The timestamps may range from thousands of years to a fraction of a second different
• CAN traffic can tend to be cyclical, so finding two windows of two files that align doesn't necessarily mean that those are the same messages
• The naive algorithm (find where two large windows are equal) is not performant